The invention relates to a circuit for conditioning sync signals for colour television sets. In particular, the invention is based on a circuit for conditioning sync signals in accordance with the preamble of Claim 1.
A particular area of application for the invention is a convergence correction circuit in a television projection device in which the pictures from three monochromatic picture tubes are projected onto a picture surface. A facility of this type serves, in principle, for the correction of parameters in the raster deflection, for example the correction of north/south and east/west distortions, of pincushion distortions, of non-linearities in the deflection and other geometrical errors in the horizontal and vertical directions. For this purpose, the convergence circuit influences the deflection parameters of each of the three picture tubes depending on the position of the luminous spot. This requires that the convergence circuit, which is frequently designed as an integrated circuit, be synchronized with the beam deflection of the individual picture tubes. The synchronization is effected by means of the pulse-like horizontal and vertical synchronizationxe2x80x94or sync for shortxe2x80x94signals which are fed to the convergence circuit. In this case, the problem arises that the phase angle of the vertical and/or horizontal sync pulses is not unambiguously defined and may vary from device to device. Noise, humming or crosstalk of the line deflection can give rise to different results in the course of the line counting because the first line pulse of the second field occurs contemporaneously with the vertical sync pulse, and the line pulse is therefore not always unambiguously identified. This leads to the position of inserted signals in a field varying by one line (xe2x80x9cline jitterxe2x80x9d).
In order to overcome this problem, it is already known in the prior art to synchronize the convergence circuit not with the vertical sync signal but with a pulse which is temporally offset by a specific quantity. This delayed pulse is temporally offset by a constant value relative to the first line pulses of the two fields, with the result that none of the horizontal line pulses then occurs simultaneously with the delayed pulse and, consequently, the influence of crosstalk or humming does not, in principle, present difficulties any longer. In this way, it is ensured that the respective pulses are always unambiguously identified. The best interference margin is given when the delayed vertical pulse lies exactly between the two first line pulses of the two fields. However, if the phase angle differs between different devices, then the optimum interference margin is no longer ensured in every device.
Taking this as a departure point, an object of the invention is to provide a circuit for conditioning sync signals which affords improved synchronization with the vertical and/or horizontal deflection of a picture tube.
This object is achieved by means of a circuit for conditioning sync signals according to Claim 1.
A fundamental concept of the invention is to provide measuring means in order to determine the timing of the horizontal sync signals relative to the vertical sync signal and/or relative to the signal delayed by the delay stage, and to design the delay stage of the circuit arrangement in such a way that the delay time is adjustable.
In accordance with a particularly advantageous development of the invention, the circuit can have computing means which enable the measurement results obtained in this way to be utilized in order to calculate a specific delay time using predetermined rules. The aim of this calculation is to avoid, for example, interference in the course of the line counting and disadvantageous effects associated therewith.
Subclaims relate to further advantageous refinements of the invention.
A further object of the invention is to specify a method by means of which improved synchronization of a circuit with the deflection of a picture tube is achieved.
This object is achieved by means of a method according to Claim 5.
The method according to the invention has the advantage that a signal delayed by a fixed period of time, with the disadvantages mentioned in the introduction, is not used. Rather, the time delay for the time-delayed signal can be continually adapted to the phase angle of the vertical and horizontal sync pulses in accordance with predetermined rules.
It is particularly advantageous if the time interval between the delayed signal and the directly leading and/or lagging horizontal sync signal is essentially identical. In this way, the optimum interference margin between the time-delayed vertical pulse and the relevant line pulses is always achieved.
However, the time delay can also be calculated in such a way that the time interval between the delayed signal and the directly leading and/or lagging horizontal sync signal is greater than temporal shifts which are caused by interference and can be estimated for example on the basis of values from experience.
Subclaims relate to the development of the method according to the invention for the purpose of displaying video frames in two fields.
Finally, an object of the invention is to provide a television set in which the synchronization of electronic circuits with the deflection is improved.
This object is achieved by means of a television set according to Claim 10.